Plastic bottles are widely used as containers for retailing soft drinks and other beverages. One type of plastic, polyethylene terephthalate (PET), has become particularly popular because of its transparency, light weight, and low cost. In addition to being flexible, the walls of PET bottles are strong in tension and thus can safely contain the pressure of a carbonated beverage. Moreover, conventional PET bottles can bear surprisingly high compressive loads, provided that the load is directed substantially along an axially symmetric axis of the bottle. A single PET bottle can support the weight of many bottles of the same size filled with beverage if the bottle is standing upright on a flat, horizontal surface and the weight of the other bottles is applied to the closure of the single bottle and is directed substantially vertically along the symmetric axis. However, if a compressive load is applied to a conventional PET beverage bottle along a direction other than the symmetry axis of the bottle, the bottle tends to buckle. This tendency of conventional PET bottles to give way under off-axis compressive loads is particularly pronounced for large capacity bottles, such as the two-liter bottle widely used for marketing soft drinks.
Soft drink bottles are ordinarily packaged by bottlers in cases or other containers, several bottles to the case, for shipment to retailers or for storage. The term "case", "crate" or "tray" is used interchangeably herein to include all cases, crates, trays and similar containers having a bottom and peripheral side wall structure. Cases of bottles are customarily stacked on top of each other. In storage warehouses, columns of cases are frequently stacked on pallets which can be lifted and moved about by fork-lift trucks. The stacks of cases on the pallets must therefore be particularly stable in order to remain standing in the face of the jostling inherent in being moved about. A technique for interconnecting stacks of empty cases, called "cross-stacking," is often used to improve the stability of empty cases loaded on a warehouse pallet. Cross-stacking generally involves stacking rectangular bottle cases to build up a layered structure, with each layer having cases oriented parallel to each other and with the adjacent layers being oriented at right angles to each other. Thus, since the adjacent layers are perpendicular, each case in the cross-stacked layer rests on at least two cases in the layer below. As a result, the cases of the cross-stacked layer tend to keep the cases on which they rest from moving apart from each other. The cross-stacked layers therefore stabilize the stacked structure.
Because of the tendency of conventional PET beverage bottles to buckle under off-axis loads, attempts to stack cases of these bottles give rise to serious problems. Bottles can tilt away from vertical alignment upon stacking if conventional partitioned cases having low side walls are used to contain the bottles. Tilted bottles in the lower cases of a stack can buckle and give way, causing the stack to fall. Even absent buckling, the tendency of bottles to tilt in conventional low-sided cases causes problems. Tilting generally places an undesirably low limit on the number of tiers in a stack since the tilting of bottles in one case can cause the next higher case in the stack to tilt. This leads to instability if too many tiers are included in the stack.
Previously, these problems were dealt with by packaging beverage bottles in corrugated-paper cartons having high sides, often equal in height to the height of the bottles. Two-liter PET bottles filled with soft drinks were often packaged in enclosed corrugated paper cartons for storage and shipment. Although the high sides of these paper cartons reduce the incidence of tilting and provide additional support when the cartons are stacked, the cartons are expensive. The cost of the cartons cannot ordinarily be distributed over a number of repeated uses since corrugated-paper cartons generally are not rugged enough for reuse and therefore they are usually discarded by the retailer.
One solution to the problems of full depth corrugated-paper cartons is plastic full depth cases; that is, plastic cases having peripheral sidewalls approximately the same height as the bottles. In plastic full depth cases, the sidewalls are the load bearing surfaces. Full depth plastic cases, however, have numerous disadvantages. They are expensive to manufacture, they are expensive to ship and to store empty in a warehouse as they require a large amount of space, and full depth cases also totally surround the bottles and prevent display of the bottles.
To overcome these problems plastic low depth cases have been used. A low depth case is one in which the side walls are lower than the height of the stored bottles, and in which the bottles support the weight of additional cases stacked on top. However, these too have drawbacks. For example, some low depth cases, require additional structure to hold the bottles and insure complete bottle stability, even though the case depth is more than 25% of the height of the bottles.
Various plastic reusable bottle carriers are known in the art. One reusable bottle carrier is disclosed in U.S. Pat. No. 3,055,542 to Russo. The bottle carrier can be made of a plastic, and is assembled from two pieces: a handle and a carrier body having six cups for soft drink bottles. In order to stack the bottle carriers when empty, the handles must be removed. This is very inconvenient and time consuming. The '542 bottle carrier is also seriously limited regarding stacking loaded carriers. It cannot be stacked in a conventional cross-stacked structure because, as illustrated therein, the spacing between the bottles in the carriers is different in the directions parallel and perpendicular to the handle of the carrier.
Kappel U.S. Pat. No. 2,970,715 is one of the earlier embodiments of molded plastic low depth bottle carrying cases. Each bottle rests on a raised flat surface within an individual compartment. The bottom of the case is formed with recesses for receiving bottle tops when loaded cases are vertically stacked. However, Kappel does not indicate the size of the carrying case relative to the bottles being carried.
In Bunnell, U.S. Pat. No. 3,812,996, a reusable plastic bottle carrying case for beer bottles is disclosed. The case is designed with a plurality of bottle compartments having flat bottom walls. The cases are designed to be cross-stacked; the cases are dimensioned so that the center-to-center distance between adjacent bottles within a case is the same as the center-to-center distance between adjacent bottles in adjacent cases in abutting relationship. Thus, the vertical axes of the bottles in adjacent layers are co-linear. Although a plurality of loaded carrying cases is designed to be vertically stackable with the weight of upper cases supported by the bottles within lower cases, the lower surface of the bottom wall of the case is flat. Thus, there is no structure for assuring a proper alignment or centering of one case with an upper or lower case.
Garcia, U.S. Pat. No. 3,247,996 discloses a plastic bottle container for milk bottles. The container is shorter than the bottles which extend above the top surface of the container walls. In Garcia, the bottles, rather than the walls of the container, are load bearing. Indented circular portions may be formed in the bottom wall to receive bottle tops when containers are vertically stacked. Like many prior art bottle carriers, the Garcia container has sides of reduced height from those of a standard full depth case; also, it can be used with a variety of bottles. However, the case is not a low depth case and is more expensive than low depth cases. It also does not have the display capabilities of low depth cases.
A more recent attempt to solve the problem of providing reusable, low depth, cross-stackable PET bottle cases is disclosed in U.S. Pat. No. 4,344,530 to deLarosiere. The '530 patent has many of the features and problems of Garcia and discloses a plastic PET bottle case that is cross-stackable and has a very low depth as shown in the figures. This low depth is disclosed as being approximately 1/6 the height of the PET bottles, or approximately 2 inches. However, in practice, this depth is insufficient because the large degree of lateral instability does not prevent bottles from tipping over. Additionally, the bottle retaining pockets are required to have a raised annular bottle seat ting which fits within the inner indentation formed in the base of many bottles to insure bottle stability. This does not permit all PET bottles to rotate within the bottle pockets for display purposes. Additionally, it does not permit one piece bottles (i.e., petaloid bottles that do not have a base indentation) to be adequately retained.
The commonly assigned U.S. Pat. Nos. 4,899,874 and 4,978,002, the contents of which are hereby incorporated by reference, disclose a low depth bottle case for two-liter bottles that is cross-stackable when empty if the upper cross-stacked cases are properly positioned. In addition, in the embodiment disclosed the substantially flat upper surface across the bottle retaining pockets permits one piece petaloid bottles and bottles with base indentations to be retained. The low height of the case sidewalls and the columns above the case sidewalls also allow the display of the bottle labels to the consumer. However, because of the low depth and the substantially flat upper surface across the bottle retaining pocket, a generally snug fit is required between the bottle pocket and the bottle and therefore, there is a limit on the range of bottle diameters which can be retained in a stable stack.
The trend in the bottling industry today is to manufacture two-liter bottles as inexpensively as possible. This means reducing the amount of plastic in the bottle, but still maintaining sufficient bottle strength to support fully loaded cases stacked thereabove. In order to accomplish this task, the newest two-liter bottles are made to have smaller diameters and a slightly greater height than their predecessors. The result is a lightweight two-liter bottle having a slimmer overall profile than previous two-liter bottles. The lightweight bottle, however, due to its slimmer profile and increased height, does not perform ideally within the bottle pockets of the low-depth two-liter cases discussed above.